Ferrous alloys and manufacture thereof



Sept. 17, 1963 E. BEDELL, JR 3,104,168

FERROUS ALLOYS AND MANUFACTURE THEREOF Filed Nov. 10, 1960 4 Sheets-Sheet 1 Sept. 17, 1963 E. 1.. BEDELL, JR 3,104,168

FERROUS ALLOYS AND MANUFACTURE THEREOF Filed Nov. 10, 1960 4 Sheets-Sheet 2 Splwarwl i1. @SAZMZJ/a.

Sept. 17, 1963 E. BEDELL, JR 3,104,168

FERROUS ALLOYS AND MANUFACTURE THEREOF Filed Nov. 10, 1960 4 Sheets-Sheet a Emma/MOP plwmhd I. QMAAXZJR.

United States Patent 3,104,168 FERROUS ALLOYS AND MANUFACTURE THEREOF Edward L. Bedell, Jr., West Allis, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed Nov. 10, 1960, Ser. No. 68,463 6 Claims. (Cl. 75126) The present invention relates generally to the manufacture of ferrous alloys and more particularly to methods for making and compositions for high temperature ferrous alloys characterized by high strength and markedly improved stress rupture properties when employed under severe operating conditions.

Various attempts have been made in the past to modify and perfect the so-called twelve percent chromium stainless steel type alloys to obtain improved high temperature properties. While these efforts have, achieved modest success, none have succeeded in creating an alloy capable of withstanding severe high temperature applications.

.Typical of the alloys of the prior art, hereinafter called PA, is the following composition:

Alloy PA possesses the temperatures indicated:

Tensile strength (X10 p.s.i.) 117-149 58. 75 Yield Strength (X10 p.s.i.) 90-125 51. 0 Elongation (percent) 22- 18.5 V 19 Reduction of area (percent) 52- 48 63 Brinell hardness 229-341 The present invention is based upon improved methods and compositions in the preparation of high temperature alloys which possess the following properties at the temperatures indicated:

Tensile strength (X10 p.s 1 135-176 75-105 Yield strength (X10 p.s.i 116-145 65- 85 Elongation (percent). 9 15- 11 Reduction of area (percent) 31- 19 45- 35 Brinell hardness 269-373 in addition to the foregoing markedly inferior properties, the prior art alloy sulfers further from its propensity to form delta ferrite throughout its matrix, to soften on tempering and to possess relatively poor stress rupture and creep resistance properties.

More particularly, the present invention is predicated following properties at the "Ice upon the discovery that a vastly improved high tempera ture alloy results from a composition consisting of (by weight percent): from at least 0.07 up to about 0.42 percent of boron; 11 to 13.5 percent chromium; 1.5 to '3 percent molybdenum; 0.50 to 2.00 percent tungsten; 0.15.

to 0.35 percent vanadium; up to 1.20 percent nickel; up to 1.20 percent manganese; 0.15 to 0.30 percent carbon; 0.55 percent silicon maximum; 0.03 percent maximum sulfur; 0.03 maximum percent phosphorus; up to 0.10

percent nitrogen; and the remainder essentially iron, in which a distinct and unique correlation between amounts of boron and molybdeum exists asshall be hereinafter described in detail.

Accordingly, the primary objects of the present invention are to provide an improved ferrous alloy of the type described which has enhanced stress rupture and creep properties at high temperatures, which resists soften-..

ing on tempering, which substantially completely eliminnates the formation of delta ferrite; which has considerably more strength and therefore may be used under more drastic design and conditions in high temperaturesand stress than has been heretofore deemed possible for this type of alloy.

These and still further objects, as shall hereinafter appear, are fulfilled by the present invention to a remarkably unexpected extent as will be discerned from the following detailed description of certain exemplary embodiments of the present invention and the accompanying drawing which includes photomicrographic comparisons between the alloy of the present invention and alloy PA.

In the drawing:

FIG. 1 is a photomicrograph from an electron micoscope (at 4400X) showing the microstructure of alloy PA;

FIG. 2 is a like (at 4400 photomicrograph showing the microstructure of the alloy of the present invention;

'FIG. 3 is a photomicrograph (at 500x) of another section of alloy PA;

FIG. 4 is a like (at 500X) Photomicrograph of the alloy of the present invention;

FIG. 5 is a photomicrograph from an electron microscope (at 45 00X) of alloy PA art showing the inclusions of the delta ferrite throughout the matrix; and

FIG. 6 is a plot of constant stress to rupture data at 1100 F. and 45,000 p.s.i. showing the significant difference existent between alloy'PA and the alloys of the present invention. 7

One practice of my invention shall now be described,

After the melt has been adjusted in the usual manneri for such elements as carbon, the boron is added justbe- The fore tapping the heat and casting it into ingots. boron is easily introduced as a ferro-alloy.

The ingots are next stripped from their molds while still hot and bedded in an insulating mass which permits the mass to slow cool (to prevent internal cracking) The raw ingots are next completely surface conditioned before forging.

To prepare the test bars for which data is herein reported, the ingots are forged into A" to 1" square sections which are cut into standard blanks for ASTM .505 tensile test bars. The bars are normally austenitized at a temperature of from 1950" to about 2100 F. tor two hours and then oil quenched. Next the oil quenched bars are tempered at about 1300 to 1350 F. for from four to about twelve hours and thereafter air cooled.

If desired, the tempering step may be followed by a stress relief anneal achieved by heating the tempered bars to a temperature of about 1225 to 1250 F. for about four to six hours and air cooled.

One of the key aspects of the present invention, though not fully understood, is the synergistic coaction developed between the molybdenum and the boron in my alloy.

Thus, I find that my improved properties are not obtained by molybdenum alone or with boron alone but, rather, when both molybdenum and boron are maintained within the limits I have already indicated.

This relationship is more forcefully developed from a consideration of Tables I and II which respectively indicate the compositions and the results when the refractory elements, viz., molybdenum, tungsten and vanadium, are varied or omitted.

Table 1 Chemical analysis of alloy (weight percent) 1 Heat Cr Mo W V Mn Ni Si B 2 C N 1:All steels contained less than 0.03 weight percent of sulfur and phos orus. p I Boron analysis determined for s-tempered condition.

All alloys of Table I were austenitized at 1,050 F. for 2 hours, all quenched, tempered at 1,350 I". for 6 hours and air quencecl.

Part of the mechanism believed to provide the remarkable properties of my alloys is an observed tendency of molybdenum to affect the status of the boron in the alloy. By this I mean I have observed two different states of boron in my alloy. One I shall call soluble boron and the other I shall call insoluble boron.

By soluble boron I mean that portion of the total boron content which is acid soluble (in 1:2 sulfuric acid) and can be recovered by distillation as methyl borate using a standard acid recovery. The borate ester may then be saponified with curcumin (Eastman Chemical Company, No. 1179), to produce a reddish brown boron curumin complex which may then be spectrophotometrically measured.

By insoluble boron I mean that portion of the total boron content which is not soluble in acid (e.g. 1:2 sulfuric acid) and which, therefore, is recovered by fusion with sodium carbonate which is thereafter saponified with curcumin into a reddish brown boron curumin complex for spectrophotometrio measurement.

By total boron I mean the arithmetic sum of the soluble and insoluble boron fractions.

I have observed that the presence of molybdenum in my alloy has a great propensity to drive boron into an insoluble condition without completely eliminating the soluble boron state. It is my present understanding that my improved physical properties are the result of the combined dispersion of this insoluble boron and of soluble boron through my matrix.

Table III, reported below, shows the change of boron state relative to molybdenum in the heats reported in Tables I and II.

Table III Partial chemical analysis 01 alloy Heat N 0.

MO B B imol Blol Further examples of the present invention are presented in Tables IV and V (Table IV reporting chemical composition of several of my alloys and Table V the physical measurements taken) to aid in a more complete understanding of the present invention. For comparison purposes, a corresponding analysis and measurements for alloy PA are included at line one of the tables.

While only one series of strength measurements were made for each heat, several stress rupture measurements were made for a number of the heats and all are reported.

A blank occurring in chemical analyses means that the element was not detected in the alloy while a blank under physical properties indicates that the measurement was not made.

Table IV Chemical analyses of alloy Heat BHN OrMoWVMnNi B C N N0rE.-Heats PA and 1 through 24 were austenltized at 1,950F. for 2 hours, oil quenched tempered at 1,350F. for 6 hours and air cooled. Heats 25 and 26 were austenltized at 1950 F. for 2 hours, oil quenched, tempered at 1,200 F. for 2 hours and air cooled. Allheatshaddn weight percent, between 0.15 and 0.55 percent silicon and less than 0.03 percent phosphorus and sulfur.

Table V-A Physical Properties of Alloy Heat Tensile strength Yield strength Elongation N o. (p.s.i. 10 (p.s.i. X10 (Percent) Room 1,100 F. Room 1,100 F. Room 1,100 F. temp. temp. temp.

Table VB Heat Stress to Time to El. Heat Stress to Time to E1. N o. rupture rupture (per- N o. rupture rupture (per- X (psi) (hrs) cent) X10 (psi) (hrs.) cent) Referring sp c'cifically to the drawing, a visual distinction between alloy PA and those of the present invention is clearly shown. Thus, a comparison of FIGS. 1 and 2 reveals that FIG. 2 definitely possesses an aggregate dispersion believed .to be an iron-molybdenum-boron intermetallic compound (which holds the boron as insoluble boron) throughout its matrix and marked X. I he finer dispersion in FIG. 2 is thought to be a borocarbide which is produced upon tempering. FIG. 11 contains only a dispersion of complex carbide resulting from tempering.

Referring to FIGS. 3 and 5, the austenitizing process causes alloy PA to retain a relatively large amount of delta ferrite upon quenching while the alloy of the present invention contains no delta ferrite as shown in FIGS. 2 and 4.

Referring to FIG. 6, thelog of the rupture time (in hours) at 45,000 p.s.i. and 1100 F. is plotted for the several heats reported in Tables IV and V and includes two alloys of the PA type indicated as PA-1 Iand PA-2. PA-l is an alloy sold by Universal Cyclops Steel Corporation and PA-2 is an alloy sold by Allegheny Ludlum Steel Corporation, both of which have compositions corresponding to the 'general PA composition defined earlier in this specification.

Heat 1, it will be recalled, reflected only a molybdenum increase without any boron and its properties are manifestly poorer than any of the heats 2 through 23 which included the novel coaction between boron and molybdenum which I consider to be one of my important contributions to the progress of this art.

The calculated mean value of rupture time for alloys PA is 3.1 hours while the corresponding mean time for the alloys of the present invention is 149.4 hours.

As is readily apparent from this description, the methods and alloys herein described introduce remarkably unexpected advantages into the metallurgical art including the manufacture of ferrous alloy having high temperature properties :to satisfy my aforestated objects to a degree beyond expectations.

It is of course understood that the procedures and alloys described and illustrated herein are intended to exemplify the present invention rather than limit it and that all modifications and variations falling within the spirit of this invention, especially as defined by the appended claims, are intended within its scope.

Having now particularly described and ascertained the nature of my said invention and the manner in which it is to be performed, I declare that what I claim is:

1. A ferrous alloy consisting of (in weight percent): 0.15 to 0.30 percent carbon; 0.07 to about 0.42 percent boron; 1.5 to 3.0 percent molybdenum; 11.0 to 13.5 percent chromium; 050 to 2.00 percent tungsten; 0.15 to 0.35 percent vanadium; up to 1.20 percent nickel; up to 1.20 percent manganese; up to 0.10 percent nitrogen; not more than 0.55 percent silicon; not more than 0.03 percent phosphorus, not more than 0.03 percent sulfur, and the remainder iron.

2. A ferrous alloy having improved high temperature properties 'as characterized at 1100 F. by a tensile strength of from about 75,000 to about 105,000 p.s.i., a yield strength of from about 65,000 to about 85,000 p.s.i., an elongation of from about 11 to about 15 percent, a reduction of area of from about 35 to about 45 percent, having a substantially tempered m-artensitic matrix devoid of delta ferrite and a chemical composition consisting essentially of: 0.15 to 0.30 percent (by weight) carbon, 0.07 to about 0.42 percent boron; 1.5 to 3 percent molybdenum, 11 to 13.5 percent chromium, 0.50 to 2.00 percent tungsten, 0.15 .to 0.35 percent vanadium, not over 0.55 percent silicon, and the remainder iron.

3. A ferrous alloy having improved high temperature properties as characterized, at 1100 'F. by a tensile strength of at least about 75,000 psi, a yield strength of at least about 65,000 psi, an elongation of at least 11 percent, a reduction of area of at least 35 percent and a tempered martensitic matrix devoid of delta ferrite, having a chemical composition, in weight percent, consisting of: 11.00 to 13.50 percent chromium, 1.50 to 3.00 percent molybdenum, 0.50 to 2.00 percent tungsten, 0.15 to 0.35 percent vanadium, 0 to 1.20 percent nickel, 0 to 1.20 percent manganese, 0.15 to 0.30 percent carbon, 0.07 to 0.42 percent boron, up to 0.10 percent nitrogen, up to 0.55 percent silicon, up to 0.03 percent sulfur, up to 0.03 percent phosphorus, and the remainder iron.

4. A ferrous alloy according to 101211 111 3 containing inclusions randomly dispersed through said matrix.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,104,168 September 17, 1963 Edward L. Bedell, Jr.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 7, line 5 for "1.30 percent nickel read 1.20 percent nickel Signed and sealed this 3rd day of March 1964.

(SEAL) Attest:

DWI EYNOLD ERNEST W. SWIDER E N L R S Attesting Officer AC ting Commissioner of Patents 

2. A FERROUS ALLOY HAVING IMPROVED HIGH TEMPERATURE PROPERITES AS CHARACTERIZED AT 1100*F. BY A TENSILE STRENGTH OF FROM ABOUT 75,000 TO ABOUT 105,000 P.S.I., A YEILD STRENGTH OF FROM ABOUT 65,000 TO ABOUT 85,000 P.S.I., AN ELONGATION OF FROM ABOUT 11 TO ABOUT 15 PERCENT, A REDUCTION OF AREA OF FROM ABOUT 35 TO ABOUT 45 PERCENT, HAVING A SUBSTANTIALLY TEMPERED MARTENSTILE MATRIX DEVOID OF DELTA FERRITE AND A CHEMICAL COMPOSITION CONSISTING ESSENTIALLY OF: 0.15 TO 0.30 PERCENT (BY WEIGHT) CARBON, 0.07 TO ABOUT 0.42 PERCENT BORON; 1.5 TO 3 PERCENT MOLYBDENUM, 11 TO 13.5 PERCENT CHROMIUM, 0.50 TO 2.00 PERCENT TTUNGSTEN, 0.15 TO 0.35 PERCENNT VANADIUM, NOT OVER 0.55 PERCENT SILICON, AND THE REMAINDER IRON. 